Laminated glass is excellently safe because it generates only a small amount of scattering glass fragments even when being subjected to external impact and is broken. Therefore, laminated glass is widely used in automobiles, railroad cars, airplanes, ships, buildings, and the like. Laminated glass is manufactured by interposing an interlayer film for laminated glass between two glass plates.
Interlayer films for laminated glass include a single-layered interlayer film having a structure consisting of a single layer and a multilayered interlayer film having a structure consisting of two or more layers.
The following Patent Literature 1 discloses, as an example of an interlayer film for laminated glass, a sound insulating layer containing 100 parts by weight of a polyvinyl acetal resin having a degree of acetalization of 60 to 85 mol %, 0.001 to 1.0 part by weight of at least one kind of metal salt among alkali metal salts and alkaline earth metal salts, and a plasticizer in an amount of greater than 30 parts by weight. This sound insulating layer alone can be used as an interlayer film.
The following Patent Literature 1 also describes a multilayered interlayer film in which the aforementioned sound insulating layer and another layer are laminated. The other layer laminated on the sound insulating layer contains 100 parts by weight of a polyvinyl acetal resin having a degree of acetalization of 60 to 85 mol %, 0.001 to 1.0 part by weight of at least one kind of metal salt among alkali metal salts and alkaline earth metal salts, and a plasticizer in an amount of 30 parts by weight or less.
The following Patent Literature 2 discloses an interlayer film which is a polymer layer having a glass transition temperature of 33° C. or higher. Patent Literature 2 describes that the polymer layer is disposed between glass plates having a thickness of 4.0 mm or less.
The following Patent Literature 3 discloses an interlayer film containing (A) polyvinyl acetal, (B) at least one kind of plasticizer, (C) fumed silica, and (D) at least one kind of basic compound. In this interlayer film, a difference in refractive index between (C) fumed silica and plasticized polyvinyl acetal (A+B) is 0.015 or less, and a weight ratio of C/(A+B) is 2.7/100 to 60/100.